A new idea for ELT antenna placement

[Sam Buchanan]

Originally Posted by jetdriven

The instructions say the antenna must be mounted within 30 degrees of vertical.

True, but where can you do that on an RV-8 and satisfy all the other requirements for a legal ELT installation?

[bret]

Why must the antenna be mounted almost vertical, if we crash, are we guaranteed to land up right on the wheel

[airguy]

Originally Posted by bret

Why must the antenna be mounted almost vertical, if we crash, are we guaranteed to land up right on the wheel

If the gov't requires you to crash upright, then you'd better crash upright or you'll be in BEEEEGGG trouble!

[Flyin'Bryan]

Originally Posted by DanH

I've heard of folks mounting them inside the wingtip. Same antenna orientation upside down or right side up, and the antenna cable doesn't pass through structure.

After 26 years of Civil Air Patrol Search and Rescue flying, I unfortunately have more experience than I wish I had with respect to the causes and end-results of many airplane crashes. See the following link for more info on this ELT antenna topic:
http://www.vansairforce.com/communit...ad.php?t=81437

In short - the wing is one of the first things to become completely destroyed in a crash situation, so this is about one of the worst locations you can choose if you expect it to provide any benefit.

I too have struggled as to where to put mine, and for the RV8 there is no simple answer. So in the end you are left with little more than to pick the best location you can with the space available that will allow the unit the best possible chance of surviving a significant impact.

I found it interesting that another poster mentioned that the NTSB accidents for RV-8s indicate that many of them end up on their backs. Without knowing the details, it sounds like these may have been ground loop or other landing-related types of problems. The truth about any airplane crash from my own personal SAR experience is that the tail section is the only part of the aircraft that is even remotely recognizeable in most cases, and is thus the reason that ELTs are usually mounted in the aft section of the airplane.

As for the antenna ground plane and adequate SWR comments, all I can say to that is that SAR pilots undergo substantial training that is conducted by using practice beacons with antennas that are configured all sorts of ways. This includes scenarios with no antenna at all, to one that is half broken off, to one that is buried 3 feet in snow, or ones with less than a full battery charge, etc. Perhaps the closest thing we ever did in training that would emmulate an antenna housed inside the fuselage is when we would put one inside a 55 gallon drum and close the lid, and then tip it over on its side.

The end is result is that sometimes you are amazed at how some of them can still be located under less than desireable circumstances. I guess my current perspective is that I am less concerned about where I put the ELT and antenna (wing excepted) as long as it is somewhere aft. I am more concerned about making sure that the ELT batteries are fully charged and replaced when they expire, and that the system is periodically tested (the right way) so I know it is working. Bad or neglected batteries, more than anything else, are the biggest reason why ELTs are rendered useless when they are needed the most.

Fly safe....

[az_gila]

As for the antenna ground plane and adequate SWR comments, all I can say to that is that SAR pilots undergo substantial training that is conducted by using practice beacons with antennas that are configured all sorts of ways. This includes scenarios with no antenna at all, to one that is half broken off, to one that is buried 3 feet in snow, or ones with less than a full battery charge, etc. Perhaps the closest thing we ever did in training that would emmulate an antenna housed inside the fuselage is when we would put one inside a 55 gallon drum and close the lid, and then tip it over on its side.

Thanks for the comments Bryan.

Was that 55 gallon drum test with 121.5 or 406 ELTs?

I know several folks have done the 121.5 "no antenna" test by accident and found that they usually work...

The shorter burst of the higher (and weaker?) 406 frequencies might be diofferent though...

[Flyin'Bryan]

Gil, unfortunately most of my experience was working with 121.5 beacons/antennas. I ceased active participation in CAP and started building my RV 8 a couple years back, just about the same time that the new 406 ELT system change-over was just starting to ramp up, so I have not been able evaluate the differences that one might expect when working with the UHF band units. That said, I would certainly expect line of sight reception to be even more of an issue while on the higher frequency band.

It is certainly one of the more challenging and interesting kinds of flying that I have ever done. There is nothing quite like flying precise search patterns while listening for the faint aural sweeps over a squelch-broken, static-filled radio, while remaining entirely focused on the smallest changes on a directional needle and a signal strength meter, while trying to differentiate between a reflective ghost signal and the real McCoy. Those pilots that are really good at it can nail your position down to within a few feet from an airplane flying overhead at 1000 feet AGL.

As for the "non-antenna" test.......Let me just say that I have also had the pleasure of showing up on someone's doorstep at 0200 to inform them that we have traced an ELT signal to that location. I even went airborne one time to track a signal emminating from a train traveling from Illinois through Denver. So yes, if the batteries are good, and even if you have not attached your antenna on your brand new 406 ELT that UPS just delivered to your door, if you knock it over on the bench while you are unpacking it from the shipping container, that might just be enough to set the SAR wheels in motion!

[DanH]

Originally Posted by Flyin'Bryan

The truth about any airplane crash from my own personal SAR experience is that the tail section is the only part of the aircraft that is even remotely recognizeable in most cases, and is thus the reason that ELTs are usually mounted in the aft section of the airplane.

In your experience, such accidents were uniformly fatal?

[smokyray]

Originally Posted by Flyin'Bryan

After 26 years of Civil Air Patrol Search and Rescue flying, I unfortunately have more experience than I wish I had with respect to the causes and end-results of many airplane crashes.

I too have struggled as to where to put mine, and for the RV8 there is no simple answer. So in the end you are left with little more than to pick the best location you can with the space available that will allow the unit the best possible chance of surviving a significant impact.

I found it interesting that another poster mentioned that the NTSB accidents for RV-8s indicate that many of them end up on their backs. Without knowing the details, it sounds like these may have been ground loop or other landing-related types of problems. The truth about any airplane crash from my own personal SAR experience is that the tail section is the only part of the aircraft that is even remotely recognizeable in most cases, and is thus the reason that ELTs are usually mounted in the aft section of the airplane.

Bryan,
Fully concur.
I spent three years in Special Ops flying the mighty OV-10 Bronco. Our tertiary mission was SAR or CSAR depending on where the search and rescue was taking place. I only performed a handful of peacetime US SAR's, all but one were GA aircraft and only one had a happy ending. Amazingly enough though, 100% had working ELT's that through satellite reception or simple triangulation were able to eventually locate the crash site, even with several buried under snow or in a "smokin' hole".
As far as RV's go. I have helped clean up five crashes and all of them (100%) were on their back. That said, I have always mounted my VHF comm antenna on the belly. I used a Co-Ax cable 2 into 1 adapter from radio shack and my comm radio and ELT both feed into my VHF radio external antenna. I have tested it and it works great. You can still transmit VHF radio with the ELT engaged and screaming away. So, the antenna is at the highest point for worst case...

My dos centavos...
V/R
Smokey

[Flyin'Bryan]

Originally Posted by DanH

In your experience, such accidents were uniformly fatal?

Dan, unfortunately yes - mostly fatal. However, I have also seen a fair number of situations where survivors are pulled from wreckage that, after having seen it, leaves you wondering how that was even possible.

I also unfortunately had many experiences where ELTs were not working for one reason or another, and post accident reports reveal that the individuals did survive for a time after the crash, only to succomb to the elements because they could not be located in time. These are the most difficult ones of all for any SAR crew member to deal with, and is the main reason I am so passionate about this subject.

As an example, even here in Colorado with the infamous Rocky Mountains, a good solid ELT signal can mean location and rescue within 1-3 hours after ELT activation, whereas no signal can turn into 1-3 days, assuming a flight plan was filed and activated and followed. With no ELT and no flight plan, it can turn into a week or more, and sometimes not even until the snow melts in the coming spring.

Originally Posted by smokyray

Bryan,
Fully concur.
I spent three years in Special Ops flying the mighty OV-10 Bronco. As far as RV's go. I have helped clean up five crashes and all of them (100%) were on their back. That said, I have always mounted my VHF comm antenna on the belly. I used a Co-Ax cable 2 into 1 adapter from radio shack and my comm radio and ELT both feed into my VHF radio external antenna. I have tested it and it works great. You can still transmit VHF radio with the ELT engaged and screaming away. So, the antenna is at the highest point for worst case...

Smokey, thank you for your service. I built a model of the OV-10 Bronco once - cool looking airplane. Wanted to ask if your belly antenna is the standard bent comm antenna that everyone is using? You have enlightened me as to another solution that I had not yet considered, so thanks for that. it may still be a bit too far forward for my liking, but I will certainly mull that one over.

[PaigeHoffart]

Originally Posted by smokyray

I used a Co-Ax cable 2 into 1 adapter from radio shack and my comm radio and ELT both feed into my VHF radio external antenna. I have tested it and it works great. You can still transmit VHF radio with the ELT engaged and screaming away.

I know of one other person that did that successfully in a Sonex. Having said that, it is an absolutely terrible thing to do to both radios. Those bnc tees aren't one way check valves. You are putting 10W of RF into your ELT everytime you transmit. Who knows if, or for how long, it will tolerate that? Will it work when you need it? If your ELT goes off, it is transmitting directly into your receiver, which can blow out sensitive components, and result in a deaf receiver. And then there are the SWR issues that can damage your transmitter. It might work for some, it might work for a while, but there's a good chance that you will damage one or both devices.